Before attempting to fix a low resolution image, it's important to check if the resolution was reduced when the image was imported into your artwork. If this is the case, you can try reverting back to the original image to work with the highest quality version possible.
If the original image was low resolution, you might consider using image editing software like Photoshop to resize them, which can make the images appear slightly sharper.
Another option is to use one of the new AI-based apps to enhance the image but keep in mind that these techniques may not be able to fully restore the image to its original quality.
Ultimately, the best way to avoid low resolution images is to capture them in high resolution to begin with. Always create your artwork at the printing size and remember to save your document as a high-resolution "print-ready" PDF.